Synthesis and characterization of polybenzimidazoles derived from tetraaminodiphenylsulfone for high temperature gas separation membranes

A series of polybenzimidazoles containing sulfonyl groups were synthesized in Eaton's reagent for high temperature H2/CO2 separation membranes. The key monomer, 3,3′,4,4′-tetraaminodiphenylsulfone, was prepared via a novel and economical synthetic route starting from 4,4′-dichlorodiphenylsulfone. These polybenzimidazoles with sulfonyl moieties had enhanced solubilities in dipolar aprotic solvents relative to the commercial Celazole® that is prepared from diaminobenzidine. Thermal gravimetric analysis showed that the materials were stable at elevated temperatures with 5% weight loss values of at least 485 °C in either air or N2. Glass transition temperatures of three polybenzimidazoles in this series were ascertained by dynamic mechanical analysis to be 438–480 °C. These sulfonyl-containing polybenzimidazoles exhibited excellent gas separation properties for H2/CO2. Polymers from tetraaminodiphenylsulfone and either terephthalic or isophthalic acid crossed Robeson's upper bound for H2/CO2.